Solid high polymer electrolyte fuel cell units are of a structure such that the desired output is obtained by stacking together multiple fuel cells. Preferred separators that divide these fuel cells are metal materials, which compared to polymer materials are stronger with respect to pressure applied at the time of stacking and are advantageous to size reduction after stacking.
Known fuel cells employing metal separators of this kind include for example {circle around (1)} JP-A-8-180883, “Solid High Polymer Electrolyte Fuel Cell” (hereinafter, Related Art {circle around (1)}), {circle around (2)} JP-A-2000-164228, “Solid High Polymer Electrolyte Fuel Cell Separator and Manufacturing Method Thereof” (hereinafter, Related Art {circle around (2)}).
In Related Art {circle around (1)}, a single cell of a fuel cell is disclosed wherein electrode films are disposed on both sides of a solid high polymer electrolyte film, these electrode films are sandwiched with for example stainless steel separators, and the edge parts of the separators are sealed with seals.
In Related Art {circle around (2)}, a single cell of a fuel cell is disclosed wherein an anode electrode and a cathode electrode are disposed on either side of a solid high polymer film, and the anode electrode and the cathode electrode are sandwiched by separators with for example stainless steel as their base material.
In the technology of the publications of Related Art {circle around (1)} and {circle around (2)}, when for example cold rolling is carried out on stainless steel to become the material of a separator to bring the stainless steel to a predetermined thickness, at the surface layer part of the stainless steel, as a result of the rolling, an abnormal layer made up of oxides and of intermetallic compounds which had been included in the stainless steel sheet, crushed to a small particle size, is formed. Because the conductivity of this abnormal layer is not good, to make the electrical contact resistance of the separator small it is necessary for it to be removed.
To do this, a separator manufacturing method having a step of removing an abnormal layer of stainless steel like this has been conceived. This technology will be described below.
With reference to FIG. 21 the main points of the manufacture of a metal separator of related art will be explained in order.
1. Abnormal Layer Removal
A metal material 400 constituting the material of a separator is rolled before being press-formed to a predetermined shape. When the metal material 400 is rolled, an abnormal layer 401 is formed at the surface layer of the metal material 400.
2. Abnormal Layer Removal Etching
The above-mentioned abnormal layer 401 is removed by etching.
3. First Passivation Treatment
To prevent corrosion of the surface of the metal material 400, a first passivation treatment is carried out and a first passivation film 402 is formed.
4. Exposure Etching
Because particulate conductors 403 . . . ( . . . denotes a plurality. The same applies hereinafter.) consisting of the above-mentioned intermetallic compounds naturally included in the metal material 400 are good electrical conductors, with the object of reducing the electrical contact resistance between the separator and an adjacent separator or electrode when the metal material 400 is made a separator and stacked in a fuel cell, exposing of the conductors 403 . . . is carried out. To perform this exposing, etching is carried out.
5. Second Passivation Treatment
After the exposing of the conductors 403 . . . , so that the surface of the metal material 400 does not corrode a second passivation treatment is carried out, and a second passivation film 405 is formed.
This completes the manufacture of the separator.
The separator manufacturing method described above will be explained in detail with reference to FIG. 22. STXXX indicates a step number.
ST101 A metal material press-formed after rolling is degreased. The process liquid is an aqueous surfactant solution, the treatment temperature is 30° C., and the treatment time is 1 minute.
ST102 The metal material is washed. The treatment time is 1 minute.
ST103 The abnormal layer formed at the time of rolling is removed by etching. The process liquid is a solution of aqua regia and a surfactant, the treatment temperature is 98° C., and the treatment time is 60 minutes.
ST104 The metal material is washed. The treatment time is 1 minute.
ST105 To prevent corrosion of the surface of the metal material, a first passivation treatment is carried out. The process liquid is 50% nitric acid, the treatment temperature is 50° C. and the treatment time is 30 minutes.
ST106 The metal material is washed. The treatment time is 1 minute.
ST107 An etching is carried out to expose the conductors in the metal material. The process liquid is a solution of 20% nitric acid and 8% hydrofluoric acid, the treatment temperature is 30° C. and the treatment time is 10 minutes.
ST108 The metal material is washed. The treatment time is 1 minute.
ST109 To prevent corrosion of the surface of the metal material a second passivation treatment is carried out. The process liquid is 50% nitric acid, the treatment temperature is 50° C. and the treatment time is 30 minutes.
ST110 The metal material is washed. The treatment time is 1 minute.
ST111 The metal material is dried. The treatment time is 1 minute.
This completes the manufacture of the separator. The total process time is 137 minutes.
In the separator manufacturing method described above, by the abnormal layer being removed chemically by etching, and by exposing of the conductors also being carried out by etching, the contact resistance of the separator is made small.
However, in the above-mentioned FIG. 22, the required time from the degreasing of ST101 to the drying of ST111 is 137 minutes in total, and because the number of process steps is large the number of different process liquids and the number of process tanks for holding the process liquids are large and much labor is taken in the temperature management of the process liquids, and consequently, to achieve productivity improvement and cost reduction of metal separators, a reduction in the above-mentioned number of process steps has been needed.
When in the above-mentioned ST103 the intended abnormal layer removal etching is not achieved, an abnormal layer remains at the surface layer of the metal material, and it is likely that this will affect the conductor exposure etching of ST107 and exposing of the conductors will not be fully effected, and when exposing of the conductors is not sufficient, when the manufactured separator is stacked in the assembly of a fuel cell, the electrical contact resistance between separators or between separators and electrodes will be large and a sufficient output of the fuel cell will not be obtained. This is the same when the intended exposing of conductors is not achieved in ST107.
To avoid this, if it can be checked during the separator manufacturing process described above whether or not the intended treatment has been achieved, the quality of the separators can be increased and the quality of the separators can be stabilized, and when the intended processing has not been carried out on a metal material the waste of continuing processing with subsequent steps can also be eliminated.
Also, the following kind of metal separator manufacturing method will be described.
FIG. 23 shows a process tank 411 filled with a process liquid 412 and a metal material 414 (a material to eventually become a separator) held in a frame-shaped member 413 immersed in this process liquid 412. 415 is a wire suspending the frame-shaped member 413.
In a fuel cell, the separator accounts for most of the cost. This is because the separator requires a structure finely formed with flow passages for fuel gas and oxidant gas and cooling water, and surface treatment to prevent corrosion by electrolytes. Accordingly, if the productivity of the separators is raised and their cost reduced, the cost of fuel cells is greatly reduced and a contribution is made to the spread of fuel cell vehicles.
In FIG. 23, for example when the metal material 414 is treated with the process liquid 412 of the above-mentioned process tank 411, (1) to quicken the treatment of the metal material 414 and also to effect it uniformly, it is effective to agitate the process liquid 412 with an agitating device, but when there are multiple process tanks 411, an agitating device must be provided for each of them, leading to increased cost, and (2) if the carrying of the metal material 414 to the process tanks 411 and the holding of the metal material 414 for the immersion of the carried metal material 414 in the process liquid 412 are not coordinated well, the flow of the production process cannot be made smooth, and the production time increases, and (3) if the number of metal materials processed at once is low, the number of units produced per unit time is low, and if this can be improved, productivity improvement and cost reduction of separators can be achieved.